Excavation into carbonate-free pyritic rock formations can occur, for examples, during construction of highways, large structure foundations, or mining of coal and/or metal ores. The exposure of the carbonate-free pyritic rocks to oxygen and water can lead to acidic pollution and subsequent harm to the environment. For example, the construction of Interstate 99 at the Skytop area in Pennsylvania and the Superfund site at the Bingham Canyon Copper Mine in Utah have resulted in acidic pollution into the environment, a contamination known as acid rock drainage (ARD). One example of the source of such pollution is shown by the following reaction wherein pyrite (FeS2) or related iron sulfides, when exposed to water and oxygen, results in the formation of goethite (FeOOH) plus sulfate ions (SO42−) and hydrogen ions (H+).2FeS2+5H2O+7.5022FeOOH+4SO42−+8H+The sulfate and hydrogen ions together represent sulfuric acid.
The ideal treatment of an excavation site is to exactly neutralize the acid produced by the weathering of pyrite and similar acid-generating minerals. However, in practice over-treatment, i.e. application of an excess amount of a composition, typically occurs. In the case of using a strong alkali-based type material, a caustic solution that can harm the surrounding environment can be formed. For example, lime kiln dust and bag house dust contain high concentrations of calcium oxide and/or hydroxide, that where supplied up to saturation of water runoff from pyrite rock and pyrite rock formations causes buffering of the pH up to near 12. Dilution of such a saturated solution by a large amount of neutral water, e.g. a ratio of 100:1 of neutral water to saturated water runoff, only decreases the pH from 12 down to near 10. A pH of 10 is still known to be highly caustic and above the range of 6-9 required for runoff by the Pennsylvania Sanitary Water Board and agencies of other states. In addition, although caustic waters do repress sulfate concentrations, leaching by such waters of aluminum, zinc and other metals from contacted rock materials can occur and further pollute any water runoff.
Therefore, there is a need to reduce and control the amount of pollution encountered when carbonate-free pyritic rocks are exposed to oxygen and water, as is common during excavation projects.